The present invention relates to a rotating disk storage device such as a magnetic disk drive, an optical magnetic disk drive, or the like and, more particularly, to a rotating disk storage device having a driving mechanism for an actuator for positioning a head at a recording medium.
With the recent progress made in the utilization of magnetic disk drives in portable apparatuses, there is a growing need for an even more compact and thinner body. A need is also pressing for a cost reduction of each individual component part. The magnetic disk drive uses an actuator that supports and positions correctly at a required position a head for reading and writing data from and to a rotating magnetic disk. Known as a driving mechanism for the actuator is a voice coil motor (VCM) that is composed of a coil, a magnet, and a yoke.
FIG. 5 of Japanese Patent Laid-open No. Hei 11-185412 shows the construction of a typical VCM, which is shown in FIG. 1(A) in this specification. Referring to FIG. 1(A), a magnetic head 14 is mounted on a leading end of a carriage 17. A coil 18 is mounted on a trailing end of the carriage 17. FIG. 1(B) is a cross-sectional view of a VCM 15 shown in FIG. 1(A), taken along line A-A of FIG. 1(A). A lower yoke 2 formed into a flat sheet shape is mounted on a mounting surface 13b′ of a base 13. The lower yoke 2 forms a magnetic path with an upper yoke 1 attached thereto by way of column supports 1a. The magnetic disk 11 is supported for rotation about a spindle shaft 12 on the base 13.
Opposing magnets 3 are respectively attached to the surfaces, opposing to each other, of the lower yoke 2 and the upper yoke 1. A gap 4 is defined between the opposing magnets 3. A magnetic flux generated by the magnets passes through a magnetic circuit formed by the gap 4, the lower yoke 2, and the upper yoke 1. The coil 18 is disposed in the gap so as to freely move therethrough. When current is allowed to flow through the coil 18, the carriage 17 acquires a driving force in a horizontal direction. The base 13 is made by an aluminum die casting for general ease of manufacturing.
As shown in the Japanese patent reference above, the upper yoke and the lower yoke make up the magnetic circuit that serves as the magnetic path for forming a magnetic field in the gap in the conventional VCM. There is a pressing need for cost reduction in magnetic disk drives, because of their expanding future applications in portable apparatuses and other reasons. To meet this mounting need, a technique is being examined for forming an iron sheet stock into a casing through pressworking, instead of using the aluminum die casting. Ways are also studied for reducing the number of parts used in the yoke circuit of the VCM in order to implement an even thinner body.